Operation of a low-beam headlight element of a vehicle is regulated by rules and limitations concerning the light distribution pattern produced by the low-beam head-light element. The operation of a low-beam headlight element is illustrated with the aid of FIGS. 1a, 1b, and 1c, where FIG. 1a shows a side view of a low-beam head-light element 100, FIG. 1b shows a top view of the low-beam headlight element, and FIG. 1c shows a schematic illustration of a light distribution pattern which is formed on a virtual screen 110 provided in a forward position from the low-beam headlight element. The virtual screen 110 is parallel with the xy-plane of a coordinate system 199, and the light distribution pattern is schematically presented as a cross-hatched area in FIG. 1c. In the exemplifying case illustrated in FIGS. 1a-1c, the low-beam headlight element 100 is suitable for left-hand traffic. The light distribution pattern is required to have a cutoff line 111 above which the intensity of the light should be sufficiently low in order to avoid glaring drivers of oncoming vehicles. Concerning the cutoff line 111, there can be for example rules which define allowed ranges for angles α and β illustrated in FIGS. 1a-1c. For example, the angle α can be required to be on the range from −0.5 degrees to +0.5 degrees and the angle β can be required to be on the range from −1.5 degrees to +1.5 degrees.
A typical arrangement for producing the cutoff line 111 in the light distribution pattern is to provide the low-beam headlight element 100 with a screen element which cuts out a portion of the light that would otherwise fall on the region above the cutoff line 111. An inherent inconvenience related to this approach is that the screen element reduces the amount of light radiated by the low-beam headlight element. Furthermore, the screen element converts at least part of the screened light into heat and thus warms up the low-beam headlight element.